Electrochemical Modification of Boron-Doped Diamond with Cu2O Nanoparticles for Photocatalytic Applications

Abstract

It is generally accepted that one of the main challenges facing our planet today is the human interfered climate change and its inseparable link to our global society’s present and future needs. Solar energy is doubtless one of the most attractive ways to deal with these issues. Water splitting by artificial photosynthesis is a favourable means of converting solar energy into transportable and end user chemical energy. Two of the major issues that remain unresolved in artificial photosynthesis are first to find a visible light absorber earth abundant semiconductor and second a robust substrate. Additionally, photon to current conversion efficiency of the current state-of-the-art semiconductor is far below the theoretical value due to undesirable charge carrier recombination loses. Cuprous oxide (Cu2O) is a naturally occurring p-type metal oxide semiconductor, is abundant and promisingly possesses a suitable band gap (2.0 eV) and energy band position that enable it to absorb solar light in the visible spectrum to produce hydrogen gas without external bias. However, Cu2O suffers from rapid charge carrier recombination losses and self-photocorrosion when comes in contact with water under illumination. The use of bimetallic alloys or core-shell metals in nanoparticle format is beneficial in two ways; protecting semiconductor from self-photo corrosion and providing short diffusion paths for electron-hole pairs enabling fast transfer to the respective redox reaction sites. Boron-doped diamond (BDD) is a potential substrate in the field of electrocatalysis due to its plethora of advantages such as wide potential window, low background current, resistance to fouling and electrocorrosion as well as its availability at a low cost when grown by chemical vapour deposition (CVD). In this work, the electrochemical modification of oxygen terminated boron doped diamond (OBDD) electrodes decorated with NiO-Cu2O nanoparticles is described. The method involves the electrodeposition of Cu2O nanoparticles on OBDD from a surfactant-free electrolyte followed by a thin coating of NiO onto Cu2O nanoparticles (Fig. 1a). The electrochemical experimental data showed that electronic effects due to the bimetallic catalysts led to higher photocurrent densities in comparison with Cu2O nanoparticles alone (Fig. 1b). In order to understand the morphology, dispersity and size of the nanoparticles, deposits were characterised by high resolution scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Figure 1 (a) SEM image of NiO-Cu2O modified OBDD electrode and (b) Linear-sweep voltammograms of the photoelectrochemical response of Cu2O and NiO-Cu2O modified OBDD electrodes, respectively under chopped light (100 mW cm-2 and on-off frequency 0.2 Hz) at a scan rate of 10 mV s-1 in 0.1 M Na2SO4 (pH 6.2). Figure 1